1. Field of the Invention
The present invention relates to a method of repeat transmission of messages in a centrally controlled communication network.
2. Prior Art
In a centrally controlled, especially cellular, radio network, a central station ZE is provided, as shown in FIG. 1, to which several terminals T1, T2, . . . can be connected. These terminals can be, for example, telephones, but also could be PCs (personal computers) or other units. This type of system operates, for example, in a link-oriented mode, i.e. prior to exchange of data with other terminals that are connected to the network or the central station ZE, at least one link or connection must be established.
Besides this connection or link in which only one terminal is operated, there are also connections or links, in which several or all terminals are simultaneously operated (Multicast, Broadcast). Complete error correction does not occur in the existing systems. However high error probabilities must be taken into account, especially in radio transmissions. Various methods have been developed to permit error sensitive transmission of data. In most cases a combination of error protective coding (Forward Error Correction, FEC) and automatic repeat requests (ARQ) are used. FEC is based on redundancies added in transmission, so that the message still can be corrected and received in the receiver without error, when it contains a few transmission errors. ARQ in contrast is based on the assumption that the receiver can establish when a message was transmitted containing errors. This is generally achieved by using an additional check sum. When the receiver detects an error, it asks the transmitter to send this data packet to it again. For this latter method a bidirectional transmission is necessarily required. ARQ has already been investigated in detail and used in many variations for different applications (high and low error probabilities optimized, as described in A. S. Tanenbaum, “Computernetzwerke [Computer network]”, Prentice Hall, Munchen, 1998, pp. 227 to 244; B. Walke, “Mobilfunknetze und ihre Protokolle [Mobil Radio Network and its Protocols]”, B. G. Teubner, Stuttgart, 1998, pp. 91 to 99; D. Petras. “Entwicklung und Leistungsbewertung einer ATM-Funkschnittstelle [Development and Performance Evaluation of an ATM Radio Interface]”, Dissertation in RWTH Aachen, 1998, Chapter 8.3, pp. 81 to 85; and D. Bertsekas, R. Gallager, “Data Networks”, Prentice-Hall, Englewood Cliffs, N.J., 1992, pp. 64 to 68. All these methods however are based on a bidirectional connection or link, i.e. generally a point-to-point link.